It is known practice for drinks to be prepared from portion packs containing food ingredients such as a ground preparation to be extracted, a powder to be dissolved or some other partially or fully soluble agglomerate. These ingredients are generally contained in special packs such as cartridges which are inserted into a device comprising a water supply, a pump capable of delivering pressure and an injection member for introducing water into the cartridge. The drink is obtained by flowing through at least one wall after the fluid pressure has increased sufficiently within the cartridge. In general, the wall is porous by nature or by tearing upon contact with piercing or tearing elements when a predetermined fluid pressure is reached inside the cartridge. The drink obtained then flows out into the container intended for consumption.
In the case of numerous hot or cold drinks, the presence of froth (or foam) is a quality that is much sought-after for reasons both of taste and of appearance. The froth is usually a dispersed liquid-gas, generally liquid-air, system which entails the presence of a fatty substance, generally provided by the food substance, and of a physical method of agitation making it possible to form the dispersed system then known as “froth”.
Certain publications relate to the production of a froth by supplying air and/or steam. However, the air is supplied at atmospheric pressure or at low pressure or alternatively is residual air; this generally detracts from the quality and quantity of froth.
For example, patent application DE 10247573 describes the increase in the amount of froth for filter coffees using an orifice positioned between the filter and the coffee storage container which sucks in ambient air because of the depression brought about by the flow.
U.S. Pat. No. 4,581,239 describes a method of infusion using sachets with successive injections of hot water interspersed with stirrings and possible contact with a gas or steam. The introduction of a gas is done at atmospheric pressure or under the pressure of a gas pump so as merely to control the time of contact between the water and the product being infused.
Patent EP 0 652 721 B1 describes a method in which a needle pierces a flexible sachet in order to inject a mixture of air and water into it, the pressure increases and the sachet tears. The air in this mixture is, in fact, residual air contained in the pipes which mixes with the water when the extraction process begins.
Patent application GB 2 363 343 describes a method for producing froth on demand from a system of the venture type. The method consists in injecting the air in a reservoir onto a liquid with a high protein content, such as milk, causing froth to form.
Injection continues after the froth has formed so as to expel it from the reservoir. The said froth is then discharged on demand via a pipe separate from the one used to obtain the drink.
Patent application US 2002/0129712 describes a method for obtaining a creamy coffee. In this method, a device makes it possible to increase the amount of froth, and does so by injecting hot water or water vapor during the purge. This method makes it possible to obtain hot drinks and requires an injection of fluid at a temperature of between 150 and 210° F.
Patent application WO 0158786 relates to a cartridge containing a compartment containing an ingredient for extracting a drink and a passage for the outflow of the drink which comprises an air inlet and means for generating a reduction in pressure of the jet of the drink. The pressures used for extraction in the compartment are of the order of 0.7 to 2 bar. This system provides a quantity of air and makes it possible to produce froth in a special arrangement of the outflow outlet. However, this system uses the depression created by the outflow of the drink through the cartridge and so the volume of air incorporated is limited. In addition, the air is provided at relatively low pressures and so the bubbles formed are large in size and the froth formed is therefore not very stable and lacks finesse. Finally, such a system makes the cartridge more complicated and expensive to produce.
Certain publications also describe the supply of air to the portion pack for purposes other than that of improving the frothing or alternatively for no particular reason. In particular, patent application EP 0 250 810 A1 describes a method of extracting closed cartridges containing roasted coffee for the preparation of drinks, in which the cartridge is prewetted with water (at a pressure of about 2 to 3 kg/cm2). Next, air is injected to aerate the bed of coffee; the air then taking up the volume and forcing the prewetting water to occupy a maximum of volume. Finally, water is injected up to a pressure of between 35 3 and 6 kg/cm2 to finish the wetting. After these three steps, water is reinjected in order to increase the pressure and pierce the cartridge, the pressure is then of the order of 6 to 16 kg/cm2. All these steps are aimed at allowing better wetting and better aeration of the coffee with a view to optimizing its flavors in the context of ground roasted coffee.
Patents EP 051247, EP 0512142 and EP 468080 describe methods in which a mixture of water and air is injected into a cartridge. The air is also residual air contained only in the pipes.
These patents or patent applications describe methods of obtaining generally hot drinks by filtration, dissolution or extraction of a food substance.
However, there is a need to improve the control of the production and quality of the froth when preparing a hot or cold drink obtained from cartridges.
This is because producing froth for drinks from cartridges is difficult, especially if the said drinks are cold or at ambient temperature, because the supply of energy needed to form the dispersed system must then be greater because of the lesser extent to which a Brownian motion is encouraged.
The volume of air available is also generally not enough to produce a froth in satisfactory quantity and of satisfactory quality.
Another problem is associated with the need to produce drinks of a significant volume and with the insufficiency of air available in the cartridge to produce froth in satisfactory quantity and of satisfactory quality. The problem is that there is a need to produce both large-volume drinks, particularly in the case of certain hot or cold milk-based specialties, while using cartridge sizes of a reasonable size. Now, some of the ingredients involved in the composition of the drinks occupy a great deal of volume in the cartridge, such as the milk powder, for example, leaving little or no headspace and therefore little gas volume available for use in frothing. In order to obtain froth, the cartridge then has to be of a larger size so that the volume of gas needed to create froth can be reserved, but this poses problems in managing cartridge sizes, in adapting the machines to suit different sizes, in the cost of the packaging materials, and raises other problems still.
In addition, by supplying air at low pressure or atmospheric pressure, the froth has a “soapy” configuration with most of the bubbles excessively large in size, which produces a foam that lacks stability. If the space available in the cartridge is small, the supply of air is then not sufficient to produce froth. In order to make froth, it is then necessary to employ mechanical stirring systems, but that makes the device and/or the cartridge far more complicated and the quality of the froth remains mediocre.